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Motored friction mean effective pressure versus engine speed for engine breakdown tests, (a) Four- cylinder spark-ignition engine.10 (6) Average results for several four- and six-cylinder DI diesel engines.9 pumping friction, piston assembly friction, valve train friction, crankshaft bearing friction, and (in Sec. 13.7) accessory power requirements.
13.6.5 Valve Train Friction
For example, measurements of valve train friction mean effective pressure for several of these valve train types showed significant variations (± 30 percent): see Fig. 13-24a.10,21 However, when the data were adjusted to a common spring load, Fig. 13-246, the low-speed friction mep values converged and the high-speed fmep differences were reduced.10
The total valve train friction can be broken down by critical contact regions: camshaft journal bearings, rocker arm/fulcrum and cam/tappet interface.
Effective methods of reducing valve train friction are: (1) spring load and valve mass reduction; (2) use of tappet roller cam followers; (3) use of rocker arm fulcrum needle bearings.
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